1. Field of the Invention
The present invention generally relates to an AD conversion method and an AD conversion circuit. More specifically, the present invention relates to an AD conversion method and an AD conversion circuit for converting plural analog signals to digital signals.
2. Description of the Related Art
One type of a battery pack uses a lithium ion battery and is installed in a portable device such as a digital camera. In the lithium ion battery, it is generally difficult to detect battery residual power using the voltage of the lithium ion battery. Therefore, the battery residual power may be measured by detecting charging and discharging currents of a battery using a microcomputer and integrating the detected charging and discharging currents.
In a battery monitoring IC for measuring battery residual power, analog signals such as a voltage, a current and a temperature are converted to digital signals and supplied to a CPU. The CPU may undertake a temperature correction for the current value measured by the CPU or the like and integrate the charging and discharging currents.
FIG. 5 schematically illustrates an exemplary AD conversion circuit. Referring to FIG. 5, an analog signal indicative of a detected temperature is supplied, an analog signal indicative of a detected voltage is supplied, and an analog signal indicative of a detected current is supplied. These analog signals are supplied to a selector 4.
A signal selecting register 5 stores a selected signal number written by software operated by a CPU. The selected signal number is supplied from the signal selecting register 5 to the selector 4. The selector 4 selects the analog signal received from the terminal corresponding to the selected signal number and supplies the selected analog signal to the AD converter.
An enable signal is written in the conversion starting register 7 from software operated by the CPU. After the enable signal is written in the conversion starting register 7, the AD converter 6 converts the analog signal supplied from the selector 4 to a digital signal and outputs the converted digital signal from the terminal 8.
Patent Document 1 discloses an AD converter including a control unit for outputting a pause signal (STBY) for providing a conversion period and a pause period based on a trigger (TG), a timing control circuit for outputting the timing signal during the conversion period, and an AD converting unit for performing AD conversion by comparing an analog signal Va with a predetermined reference voltage by a comparator.
However, in this AD converter, the signals are selected and the AD conversion is started after software running in a CPU instructs to do so. Therefore, in order to perform the AD conversion, the CPU is operated to thereby increase power consumption. Further, there is a problem that the amount of programs of the software increases. [Patent Document 1] Japanese Laid-open Patent Publication No. 11-31968